Research On Recycling And Reuse Of Spent LiFePO₄ Cathode Materials

Olivine lithium ion phosphate (LiFePO4) stands out as one of the most promising cathode materials for LIBs system owing to its high energy density, non-toxicity, low cost and excellent chemical stability. In recent years, LiFePO4 material has been industrialized and widely used in transportation systems including electric vehicles (EVs) and hybrid electric vehicles (HEVs) and is expecting rapid expansion for the next decades. Considering the ever increasing LiFePO4 batteries holdings on overall world market and the average life span of LiFePO4 batteries, spent LiFePO4 batteries may soon become a serious problem. To address the issue about spent LiFePO4 batteries, following researches were carried out to recycle and reuse of spent LiFePO4 cathode materials in lithium-ion batteries.Recycling spent LiFePO4 cathode material by acid leaching-solvothermal method:Through the discharge, dismantling and separation process, the spent batteries were recycled in sorts and the metal packaging material, cathode and anode material, and seperator were obtained, respectively, the FePO4-2H2O hierarchical microspheres were obtained by leaching spent LiFePO4 cathode materials with phosphoric acid solution (H3PO4) and followed by subsequent solvothermal treatment, then a carbothermal reduction method was adopted to prepare LiFePCVC product by calcining the obtained FePO4·2H2O precursor with Li2CO3 and glucose in N2 atmosphere. The as-prepared LiFePO4/C sample inherits the hierarchical microsphere structure of the FePO4·2H2O precursor, with a diameter of 3-4μm. Electrochemical test indicates that the as-prepared LiFePO4/C samples exhibit excellent electrochemical performance as cathode materials in lithium-ion batteries. Their specific discharge capacity can reach 160.5 mAh g-1 at 0.1 C rate, and 82.1 mAh g-1 even at 20 C rate. After 500 cycles at 0.5 C, they still can deliver a discharge capacity of 133.5 mAh g-1 with a high capacity retention rate of 93.6%.Recycling spent LiFePO4 cathode material by acid leaching-crystallization method:the spent LiFePO4 cathode active materials were leached by phosphoric acid solution followed by subsequent crystallization reaction treatment for obtaining hierarchical FePO·2H2O micro-flowers, then the re-synthesized LiFePO4/C were prepared using the as synthesized FePO4·2H2O) as raw material via carbon thermal reduction with Li2CO3 and glucose in N2 atmosphere. The re-synthesized LiFePO4/C sample inherits the hierarchical micro-flowers structure of the FePO4-2H2O precursor, with a diameter of 1-2μm. Electrochemical test indicates that the re-synthesized LiFePO4 have excellent electrochemical performance as cathode active material. The discharge capacity can reach 159.3 mAh g-1 at 0.1 C rate and 86.3 mAh g-1 even at 20 C rate, respectively. After 500 cycles at 5 C, they still have a high capacity retention rate of 95.4%. In addition, lithium was also recovered in the form of LiH2PO4 from the filtrate after collecting the FePO4·2H2O precipitate.Regenerated spent LiFePO4 cathode materials by refilling lithium in solid phase method:spent LiFePO4 cathode materials were regenerated after calcination in N2 atmosphere to refill different molar weight of Li2CO3 in solid phase method. The electrochemical test results show that the regenerated LiFePO4/C materials can effectively make up for the loss of reversible lithium by refilling 10% molar weight of Li2CO3 and exhibit excellent electrochemical performance as cathode materials in lithium-ion batteries. Their specific discharge capacity can reach 157 mAh g-1 at 0.1 C rate, and 73 mAh g-1 even at 20 C rate. The discharge capacity has no decay after 200 cycles at 0.5 C rate.Re-synthesized LiFePO4 cathode materials by calcination-reduction method:the spent LiFePO4 anode materials were re-synthesized after high temperature reduction by adding different molar weight of Li2CO3 in solid phase method, which were firstly oxidized to Li3Fe2(PO4)3 and Fe2O3 for removing the impurities. The electrochemical test results showed that the re-synthesized cathode materials can effectively make up for the loss of reversible lithium by adding suitable amount of 10% molar weight of LiaCO3 and exhibit excellent electrochemical performance as cathode materials. Their specific discharge capacity can reach 158.3 mAh g-1 at 0.1 C rate, and 97.1 mAh g-1 even at 20 C rate. After 1000 cycles at 10 C, they still can deliver a discharge capacity of 92 mAh g-1 with a high capacity retention rate of 91%.In conclusion, several methods have been explored to recycle spent LiFePO4 cathode materials. The resynthesized or regenerated LiFePO4/C materials exhibit excellent electrochemical performance as cathode active materials for lithium-ion batteries. These pilot studies provide facile and effective routes for large scale recovery and reuse of spent LiFePO4 cathode materials in lithium-ion batteries.